Commutators are rotating electrical connectors which are widely used on electric motors such as universal motors and brush type permanent magnet direct current (PMDC) motors to transfer electrical power between the stationary stator of the motor and the rotating rotor.
Cylindrical and planar are types of commutators. A cylindrical (or round) commutator is made of insulated axially-oriented conductive segments. A planar (or flat) commutator is made of insulated radially-oriented conductive segments. Electrical contacts, typically in the form of brushes, rub or slide on the rotating commutator segments to make the electrical connection. The segments are connected to the windings wound on the rotor core of the motor, and thus act as a rotary switch in order to reverse the electrical current. In a DC electric motor, the switching causes the generated magnetic field to reverse, thus allowing the motor to keep turning.
The wire of the windings on the rotor core is traditionally copper, since copper is a good electrical conductor and is reasonably robust. However, due to increasing cost, alternatives are being researched.
One such alternative is aluminium. Aluminium is a cheap alternative to copper, but is reasonably fragile. The wire can be wholly formed from aluminium, or can be an aluminium core with a copper coating, for example a copper clad aluminium (CCA) wire. When connecting a lead wire of an aluminium winding to the tang of a commutator segment, it is more common that the aluminium wire is damaged and severed as the tang is crimped or folded onto the wire and fused. This leads to a far higher scrap rate during production of the motor, which is not cost-effective.
An attempt to reduce the scrap rate uses a commutator which has tangs with a predetermined minimum spacing when folded, designed to prevent crushing and severing of the aluminium wire. This works relatively well in preventing the severing of the wire but for CCA wire, the copper cladding often tears or cracks leading to exposure of the aluminium core resulting in corrosion and eventual failure. The copper/aluminium interface between an aluminium wire connected to a copper tang is also subject to a high level of corrosion.
The present invention seeks to provide a solution to this problem.